Method and apparatus for bridge construction



METHOD AND APPARATUS FOR BRIDGE CONSTRUCTION Filed Aug. 19, 1955 J. P.MURPHY April 3, 1962 '7 Sheets-Sheet l ii-.3 I

w E m@ M m U m /A w M JNV April 3, 1962 J. P. MURPHY 3,027,633

METHOD AND APPARATUS FOR BRIDGE CONSTRUCTION Filed Aug. 19, 1955 '7'Sheets-Sheet 2 INVENTOR. J Phi/[p Murphy 1477 ORA/E V5 April 3, 1962 J.P. MURPHY 3,027,633

METHOD AND APPARATUS FOR BRIDGE CONSTRUCTION 14 7' TORNE Y5 METHOD ANDAPPARATUS FOR BRIDGE CONSTRUCTION Filed Aug. 19, 1955 J. P. MURPHY April3, 1962 '7 Sheets-Sheet 4 F'IE E INVENTOR J. P/7///,0 Murphy ATTORNEYJ'FllEi ll::l

April 3, 1962 J.P.MURPHY METHOD AND APPARATUS FOR BRIDGE CONSTRUCTIONFiled Aug. 19, 1955 FIE E 7 Sheets-Sheet 5 INVENTOR. J. Ph/Y/p MurphyQTTORNE VJ April 3, 1962 J. P. MURPHY 3,027,633

METHOD AND APPARATUS FOR BRIDGE CONSTRUCTION Filed Aug. 19, 1955 7Sheets-Sheet 6 FIE J E J. hi/L0 Murphy METHOD AND APPARATUS FOR BRIDGECONSTRUCTION Filed Aug. 19, 1955 J. P. MURPHY April 3, 1962 7Sheets-Sheet '7 F'lE ll PlE lE| INVEN TOR. J Ph/Y/p Murphy BY 1477'ORA/E VJ United States Patent 3,027,633 METHOD AND APPARATUS FOR BRIDGECONSTRUCTION John Philip Murphy, Piedmont, Califl, assignor, by mesneassignments, to Yuba Consolidatedlndustries, Inc., San Francisco,Calif., a corporation of Delaware Filed Aug. 19, 1955, Ser. No. 529,529

14 Claims. (Cl. 29-429) This invention relates generally to a method andapparatus for bridge construction and more particularly to.

a method and apparatus for constructing bridges without the use offalsework.

Heretofore, bridge .spans for bridges have been erected by assemblingthe bridge span in place upon-a falsework platform. However, inconstructing a high level bridge span, the use of falsework supported bytemporary pile bents is uneconomical because of the pile lengthsrequired. Bridge spans have also been erected by preassembling thebridge spans on barges and floating them into position. high levelbridge because the steel bridge span assemblies are too heavy foreconomical hoisting operations. Floating the bridge span in at a highlevel is not feasible both from economic and engineering aspects. Steelbridge spans that eventually become part of a bridge have beenused astemporary erection spans or working platforms but such a method islimited to a span that is relatively light and wherein the top chord ofthe. span is flat. Such a method is also limited to a span which hasbeen designed to support the load upon its top chord and wherein thespans ultimate position is relatively close to thewater.

In general, it is the object of 'the present invention to provide amethod and apparatus for bridge construction which avoids the use of atemporary falsework supported by piling or the use of a permanent spanwhich evenutlly becomes a part of the bridge.

Another object of the invention is to provide a method and apparatus forbridge construction of the above character which facilitates erection ofthe bridge spans.

Another object of the invention is to provide a method and apparatus forbridge construction of the above character in which a temporary erectionspan is supported between the bridge piers and utilized as a workingplatform for erecting the bridge spans.

Another object of the present invention is to provide a method andapparatus for bridge construction of the above character in which theerection span is erected on a barge, floated to the bridgepiers, andhoisted into position.

Another object of the invention is to provide a method and apparatus forbridge construction of the above character in which the temporaryerection span is fabricated from a material lighter than steel tofacilitate hoisting of theerection span.

Another object of the invention is to provide a method and apparatus forbridge construction of the above character in which means are providedto establish and maintain camber in the lower chord of the bridge spanas the erection span is deflected by the progressive loading of theerection span by the progressive erection of the bridge span upon theerection span.

Another object of the invention is to provide a method and apparatus ofthe above character in which additional safety features are provided.

Another object of the invention is to provide a method.

and apparatus of the above character in which the erection span is usedas a tie member to pull the bridge piers towards each other or to pushthe bridge piers away from each other to facilitate securing the endportions of the bridge span to the bridge piers.

Another object of the invention is to provide appa- This isobjectionable in constructing a.

3,027,533 Patented Apr. 3, 1962 ice ratus for bridge construction of theabove character in which supporting bents are secured to the bridgepiers to give vertical supportto the erection span.

Another object of the invention is to provide apparatus for bridgeconstructionof the above character in which means are provided forsecuring the supporting bents to the bridge piers wherein lateral loadsare transferred to the bridge piers.

.A further object of the invention is to provide apparatus for bridgeconstruction of the above character in whichmeans are provided on thesupporting bents to eliminate bending moment.

A still further object of the invention is to provideapparatus.forbridgeconstruction of the above character in appear frornthefollowiug description in which the preferred embodiment has been setforth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

FIGURE 1A is. anisometric view of the fabricated erection span restingon a barge and being towed into position.

FIGURE 1B is an isometrieview of the erection span after it has beentowed into a position adjacent the bridge piers and shows the derrick.barge coming into position.

FIGURE 1C is an isometric view showing the temporary erection span beinghoisted into position by a traveler mountedon the completed bridge spansand the floating derrick barge.

FIGURE 1D isanisometric view showing the erection spansupported betweentwo bridge piers and the beginning of the erection-of the, bridge spanin a region overlying the erection span.

FIGURE IE is an isometric view showing the bridge span almost completelyassembled by the traveler.

FIGURE. 1F is an isometric view showing the lowering of the erectionspan onto the barge by the. traveler.

FIGURE 2 is an enlarged elevational view showing the erection spaninthree positions, one position being shown in dotted lines, as it isbeing hoisted from the barge and lowered onto the supporting bentssecured to the bridge piers.

FIGURE 3 is aplan view of the hoisting operation taking place in FIGURE2 and shows the erection span in two positions, one position being shownin dotted lines.

FIGURE 4 is an enlarged side elevational view of the erection span.

FIGURE 5 is an enlarged cross-sectional view taken along the line 55 ofFIGURE 4.

FIGURE 6 is an enlarged cross-sectional view taken along the line 6-6 ofFIGURE 4.

FIGURE 7 is an enlarged cross-sectional view taken along the line 77 ofFIGURE 4.

FIGURE 8 is an enlarged side elevational view showing the erection spanas it is being lowered onto the barge after completion of the bridgespan.

FIGURE 9 is a chart showing the camber in the bridge span and thereverse camber in the erection span after the bridge span has beencompleted but before it has been swung between the bridge piers.

FIGURE 10 is a chart showing the cambers in the bridge and-erectionspans after the bridge span has been swung.

FIGURE 11 is an enlarged partial side elevational view showing thebridge span supported upon the erection span by jacks and blocking meanswhich are used to provide andmaintain camber in the bridge span.

FIGURE 12 is an enlarged side elevational view of the blocking means.

' of the erection span from the barge.

FIGURE 13 is a front elevational view of the blocking means shown inFIGURE 12.

FIGURE 14 is a side elevational view of the jacks.

FIGURE 15 is a cross-sectional view taken along the line 15 15 of FIGURE14.

The method and apparatus I have used for the erection of high levelbridge spans can best be understood by reference to the drawing. Let itbe assumed that a plurality of bridge piers have been erected upon anunderwater formation and that each consists of a foundation portion 16aand a tower or column portion 10b, the column or tower portion extendingfor a substantial distance above the water. Let it also be assumed thatit is desired to erect a bridge span on top of and interconnec-tingthebridge piers. A temporary erection span 11 is first fabricated on shoreor on one or more barges 12. If fabricated on shore it is loaded ontobarges after which the barges are towed to the site where the bridgespan is to be erected. I

The erection span may be fabricated from any suitable material butpreferably from a material substantially lighter than steel such asaluminum to facilitate hoisting The erection span may be constructed inany suitable manner well known to those skilled in the art of bridgebuilding. For example it may be comprised of a pair of'trusses framedtogether by top and'bottom lateral systems. The trusses may be made upof a plurality of individual panels which are tied together. Preferablythe trusses of the erection span are spaced on centers which areidentical to those of the permanent steel spans which are to be erectedoverlying the erection span.

After fabrication of the erection span has been completed and it hasbeen towed to the span site into a general position adjacent the piers10 as shown in FIGURE 18, a derrick barge 16 is brought into positionadjacent to the end portion 11a of the erection span and the derrick 16aof the derrick barge is connected to that end of the erection span forhoisting the same.

A deck traveler 17 equipped with two stiff-leg derricks 17a and 17b ismounted on bridge spans 18 and moves on skid-beams (not shown) mountedon the upper floor beams of the completed bridge span. Both of thestiff-leg derricks 17a and 17b are connected to end portion 11b of theerection span for hoisting that end of the erection span.

Before the erection span is hoisted, supporting falsework bents aresecured to the bridge towers. The supporting falsework bents as shownparticularly in FIGURE 2, consist of a framework 19 which has its lowerend pivotally connected to base shoes 21 by pins 22 and its upper endpivotally connected to beam shoes 23 by pins 24. The base shoes rest onthe foundation portion 10a of the bridge piers. The beam shoes are fixedto a seat beam 26 which is secured to the towers.

The bents may be fabricated from any suitable material such as wood orsteel and may be made up in sections which are adapted to be assembledto secure supporting bents of different lengths. The supporting bentsare substantially vertical and provide vertical support only but aresecured to the bridge towers 10b by a seat beam 26 to provide lateralsupport. The pin-connected shoes serve to eliminate bending moment tothe supporting bents.

The seat beam 26 may also be connected to a pair of supporting bents onthe opposite side of the bridge tower, as shown in FIGURE 2, to providesupport for an erection span when erecting the next bridge span. This isparticularly advantageous when two or more erection spans are beingutilized.

A pair of shoe seats 27 are mounted within the framework of each end ofthe seat beam 26. Each of the shoe seats has a conical recess 28 whichis adapted to cooperate with conical shoes 31 and 32. Shoes 31 and 32are connected to opposite end portions 11a and 11b respec- 4 tively ofthe erection span and are adapted to seat or nest within the shoe seats27.

Shoes 31 are pivotally connected to the lower end of a substantiallyvertical framework 33 by pins 34 and the upper end of framework 33 ispivotally connected to the erection span 11 by pins 36 and dependstherefrom.

Suitable means are provided for moving each of the shoes 31longitudinally of the erection span for purposes hereinafter described.Such means may consist of a toggle assembly 37 comprised of a pair ofupper links 38- and a pair of lower links 39 which each has one pair ofends pivotally connected to the framework 33 by a pin 34. The other pairof ends of links 38 is pivotally connected to a block 41 by a pin 42. Apair of upper links 43 has one pair of its ends pivotally connected tobloc'k41 by the same pin 42. However, the ends are spaced from links 38by pipe sections '44 mounted on pin 42. The other pair of ends of links43 is connected to a structural member 46 which is a part of the endportion 11a of the erection span by a pin 47.

The other pair of ends of links 39 is pivotally connected to a block(not shown) immediately below block 41 by bly.

A rod 54 is provided with two threaded portions 54a and 54b, portion5412 being threaded in an opposite direction to portion 54a. Portion 54ais threaded through block 41 which is carried between links 38 and 43and portion 54b is threaded into the block (not shown) which is carriedbetween links 39 and 51.

Rod 54 is held in position by a stay assembly '58 which is connected tostructural member 46. Rod 54 is journalled in the stay assembly 58 andis connected to a flexible coupling 61 which is connected to a shaft 62.Shaft 62 is connected to another flexible coupling 63. Coupling 63 isconnected to a shaft 64 and extends into a housing 66 in which suitablemeans are provided for rotating the shaft 64 and the rod 54. Such meansmay consist of connected to the erection span.

a reduction gear assembly operated by a 'hand crank or an electricallydriven motor.

It will be apparent that as the rod 54 is rotated in one direction byshaft 64 that the blocks mounted on the rod will be moved toward eachother causing the shoe 31 to be moved longitudinally of the erectionspan away from the erection span and that when the rod 54 is rotated inan opposite direction the blocks threaded on the rod will be moved awayfrom each other to cause the shoe 31 to be moved longitudinally of thespan towards the erection span. Thus, by rotating shaft '64 it ispossible to move shoe 31 longitudinally of the erection span within arange dependent upon the size of the toggle assembly 37.

Shoes 32 are pivotally connected to the other end portion 11b of theerection span by pins 71 mounted in the lower end of a verticalframework 72 depending from the erection span. It will be noted that, inthis instance, the vertical framework 72 is fixed but if desired it maybe pivotally connected to the erection span in much the same manner thatthe vertical framework 33 is pivotally Suitable means may also beprovided such as the toggle assembly 37 for moving the shoes 32longitudinally of the erection span.

Assuming that the supporting bens 15 are in position and the stiff-legderricks 17a and 17b of the traveler 17 have been connected to endportion 11b of the erechas been connected to end portion 11a of theerection span, the erection span is then hoisted in a substantiallyhorizontal plane. However, it must be hoisted at an angle with thecenter line of the bridge as shown in FIGURE 3 in order to clear thesupporting bents 15. After the erection span has been lifted above thesupporting bents, the derrick barge is used to swing the erection spanover the supporting bents. The erection span is then lowered until theshoes 31 and 32 are generally adjacent the shoe seats 27. End portion11a of the erection span is then lowered and if the shoes 31 are not invertical alignment with the adjacent shoe seats, the toggle assemblies37 are adjusted to shift the shoes longitudinally of the erection spanas hereinbefore described until the shoes 31 lie immediately above theshoe seats 27. If the adjustments provided by the toggle assemblies 37are not suificient, the bridge towers 101; are flexible enough so thatthey may be pulled with cables to provide the additional movementrequired. End portion 11a is then lowered until the shoes 31 nest withinthe recesses 28 of the adjacent shoe seats 27.

After the erection span is in place, the toggle assemblies 37 areadjusted to a neutral position, that is intermediate the two extremepositions so that they can be used later for securing the steel bridgespan to the bridge piers as hereinafter described.

When no bridge spans are yet in place, the normal procedure for erectingthe first bridge span is to erect the first few members in the bridgespan in a region overlying the erection span by the use of the derrickbarge 16 after which the traveler 17 is mounted on the erected members.The remaining members of the bridge span may then be erected upon theerection span by use of the traveler and the derrick barge may be usedfor other tasks. The traveler moves along the upper deck of the bridgespan as the erection of the bridge span progresses. It is then used forerection of subsequent bridge spans without the aid of the derrick bargeas shown in FIG- URE 1D.

During the erection of the bridge span upon the erection span, it isnecessary to build camber into the bridge span as is well known to thoseskilled in the art of bridge building. In my method of erection, this iscomplicated by the fact that both the bridge span and the erection spanmove horizontally and vertically between the unloaded condition and theloaded condition. Additional complications occur because the materialused in the erection span has different structural properties from thematerial used in the bridge span. For example, if aluminum is used inthe erection span, it is apparent that the deflection of the aluminumspan will be greater than the deflection of a comparable steel erectionspan under the same load.

In FIGURES 9 and I have shown charts utilized for constructing arepresentative steel bridge span upon an aluminum erection span. Curve76 of FIGURE 9 represents the center line of the lower chord of thesteel bridge span and shows the camber in the bridge span after it hasbeen erected upon the erection span but before it has been swung, thatis before it has been fastened to the bridge piers and allowed to carryits own weight. Curve 77 of FIGURE 9 represents the center line of theupper chord of the aluminum erection span and shows the reverse camberin the erection span after it has been loaded with the erected bridgespan.

Curve 78 of FIGURE 10 represents the center line of the lower chord ofthe steel bridge span and shows the camber in the bridge Span after thebridge span has been swung, i.e. allowed to carry its own weight. Curve79 of FIGURE 10 repersents the center line of the upper chord of thealuminum erection span showing the camber of the erection span in anunloaded condition after the bridge span has been swung.

To provide and maintain the desired camber in the bridge span as it isbeing erected upon the erection span, the panel points 85 along thelower chord of the bridge span are supported by a series of jacks 86 anda plurality of blocking devices 87. It was found desirable to supportevery other panel point with jacks 86 and the remaining panel pointswith blocking deviecs 87, however, other arrangements may be foundsuitable.

The blocking devices 87 are shown in detail in FIG- URES 12 and 13 andeach consists of a base member 91 formed of any suitable material suchas wooden blocks and which rests on the top chord of the erection span11. A top member 92 is also formed of a suitable material such as woodenblocks and is provided with a graphite contact member 93. A graphiteslab 94 rests on the graphite contact member 93 and is fixed to a pairof bars 96 which are secured to the bridge span at panel points by hooks97. A pair of wedges 98 are adapted to be driven into the space betweenthe base member 91 and the top member 92. As is well known to thoseskilled in the art, as the bridge span is pushed inwardly by the jacks86 the wedges 98 can be driven inwardly to give proper support to thepanel points 85.

One of the jacks 86 is shown in detail in FIGURES 14 and 15 and consistsof a plunger 101 mounted within a hydraulic cylinder 102. The hydrauliccylinder is mounted on a base 103 and rests on a plurality of rollers104 which have their ends 105 journalled into bars 106. The rollers 104are supported by and are adapted to move longitudinally within aU-shaped framework 107 which is secured to the erection span 11. Stops108 are provided to limit the longitudinal movement of the jack 86within a predetermined range for a purpose hereinafter described.

The plunger 101 of the jack is adapted to engage a plate 109 which isfixed to the bridge span at alternate panel points 85. A pair of bars111 are loosely mounted in the plunger 101 and engage grooves 112 inplate 109 to prevent movement of the plunger 101 relative to the plate109.

The hydraulic jacks 86 are connected by piping (not shown) to a sourceof hydraulic fluid under pressure and to means (not shown) forindividually operating each hydraulic jack.

During the erection of the bridge span, the jacks and the blockingdevices are raised to the proper elevation so that the desired camber isbuilt into the bridge span. As the various members of the bridge spanare put into place, substantially all of the bottom chord rivets aredriven. All the other joints are bolted and pinned with varying numbersof the holes filled depending upon the importance of the connection. Thedeflection of the erection span will increase as the bridge span iserected on the erection span. The jacks and blocking devices are raisedto compensate for this increased deflection to maintain the desiredcamber in the bridge span.

The lower chord of the bridge span will move horizontally because oftemperature changes and also because of vertical movement of the bridgespan. The rollers 104 on jacks 86 allow horizontal movement of the jacksand the graphite members 93 :and 94 on the blocking devices 87 allowhorizontal movement of the top members 92.

After all the members for the bridge span are in place, the bridge spanis ready to be connected to the bridge towers or columns. The bridgespan is checked again for proper camber.

The ends of the bridge span are then secured to the bridge towers.However if this cannot be done because of the spacing between the piers,the piers can be adjusted horizontally by operating the toggleassemblies 37 on the erection span. The toggle assemblies workingthrough the supporting bents 15 actually pull the bridge towers towardeach other or push the bridge towers away from each other.

Following horizontal adjustment of the bridge towers, a suitableconnection such as a pin connection is made between the ends of thebridge span and the bridge towers.

The toggle assemblies are then broken or released. The blocking devices87 are removed and the jacks 86 are slowly relieved allowing the bridgespan to gradually support its own weight, which is called swinging thebridge span. In the process of relieving the jacks, the erection spanwill move upwardly to its unloaded camber which will result in a topchord shortening of the erection span. As the load is picked up by thebridge span, it is deflected downwardly but a camber still remains inthe bridge span as shown in FIGURE 10.

After the bridge span has been swung, steps may be taken to remove theerection span. First the jacks are removed. Each end of the erectionspan is lifted from the supporting bents by the traveler and secured tothe bridge span after which the supporting bents 15 are removed. Theerection span is then slowly lowered by the traveler onto an awaitingbarge. One stifi-leg derrick of the traveler working through sheavearrangement 113 is used for lowering end 11a of the erection span andthe other stilt-leg derrick working through sheave arrangement 114 isused for lowering the end 11b of the erection span. After the erectionspan has been lowered onto the barge it may be towed to the nexterection site where it can be utilized for the erection of the nextbridge span. To insure continuity of operation, two or more erectionspans may be utilized on the same project.

The procedure and apparatus employed to carry out my invention greatlyfacilitates the erection of bridges in deep water where shippingchannels are required. This is particularly true whenever the bridgespans are relalatively long and are at a substantial elevation above thewater.

For example, in constructing a recent bridge, wherein some of the bridgespans were as much as 170' above mean sea level and wherein the steeltruss bridge spans were 289 long, various conventional methods oferecting the bridge spans had to be ruled out because of the high levelof the bridge and because of the excessive weight (over 450 tons) of thesteel truss spans. An erection span 280 long was constructed of aluminumwith a truss depth of 36 and with the trusses spaced on 42 centers (thesame as the permanent steel bridge spans). It was found that such anerection span weighed 117 tons which was less than one-third of what theequivalent steel truss span would havbe weighed. The 117 ton erectionspan was easily hoisted itno position with equipment utilized for otherphases of the erection work and therefore no heavy and expensive derrickbarges had to be constructed for lifting the 450 ton steel bridge spans.

The 280' aluminum erection span moved upwardly 11 /2 inches at itsmidpoint from a loaded to an unloaded position. The upward movement ofthe aluminum erection span was accompanied by its top chord shorteningof 3 inches. As the steel bridge span picked up its own load, itdeflected downwardly 2 inches at its midpoint.

in an unloaded position the span had a 7 inch camber at its midpoint andin the loaded position it had a 4 /2 inch reverse camber at itsmidpoint. The 289' steel bridge span had a 5% inch camber before it wasswung and a 3% inch camber after it had been swung.

It is apparent that I have provided a new method and apparatus forerecting bridge spans. The method and apparatus can be used for erectingcontinuous spans, cantilever spans, arch bridges and other likestructures. The use of the lightweight erection span greatly facilitatesthe erection of the bridge spans and eliminates the necessity oftransporting the bridge spans at a high level or hoisting them to thetop of the bridge towers. The erection span also gives greater safety tothe workmen. It provides a better support for the permanent members ofthe bridge span as they are erected on the erection span. It also makesit convenient for placing and transferring safety nets on the permanentbridge span.

I claim:

1. In a method for the construction of a permanent bridge span betweenadjacent bridge piers, the method comprising the steps of moving anerection span into a general position adjacent the bridge piers, theerection span being fabricated of a relatively light material incomparison to steel, hoisting the erection span to a predeterminedheight, securing the end portions of the erection span to the adjacentbridge piers, progressively constructing the permanent bridge span in aregion overlying the erection span, supporting the bridge span at panelpoints along the length of the bridge span upon the erection span,providing a camber in the lower chord of the bridge span, connecting theend portions of the bridge span to the adjacent bridge piers, removingthe support for the bridge span from between the bridge span and theerection span and allowing the bridge span to carry its own weight,disconnecting the end portions of the erection span from the bridgepiers, and lowering the erection span between the bridge piers.

2. A method as in claim 1 together with the steps of compensating forthe downward deflection of the erection span caused by the weight of thebridge span, the deflection in the erection span being greater than thedeflection in a comparable steel span.

3. In a method for the construction of a permanent bridge span betweenadjacent bridge piers, the method comprising the steps of moving anerection span into a general position adjacent the bridge piers, theerection span being fabricated of a relatively light material incomparison to steel, hoisting the erection span to a predeterminedheight, securing the end portions of the erection span to the adjacentbridge piers, progressively constructing the permanent bridge span in aregion overlying the erection span, supporting the bridge span upon theerection span a panel points on the bridge span, providing a camber inthe lower chord of the bridge span compensating for the deflection inthe erection span caused by the weight of the bridge span upon theerection span to maintain the camber in the bridge span, connecting theend portions of the bridge span to the adjacent bridge piers, removingthe support for the bridge span from between the bridge span and theerection span and allowing the bridge span to carry its own weight,disconnecting the end portions of the erection span from the adjacentbridge piers, and lowering the erection span between the piers.

4. In a method for the construction of a permanent bridge span betweenadjacent bridge piers, the method comprising the steps of moving anerection span into a general position adjacent the bridge piers, theerection span being fabricated of a relatively light material incomparison to steel, hoisting the erection span to a predeterminedheight, securing the end portions of the erection span to the adjacentbridge piers, progressively constructing the permanent bridge span in aregion overlying the erection span, supporting the bridge span upon theerection span at panel points of the bridge span along the length of thebridge span, providing a camber in the lower chord of the bridge span,maintaining the camber in the bridge span as the erection span isprogressively loaded by the weight of the bridge span, the deflection ofthe erection span increasing in a greater proportion than the deflectionin a comparable steel span, connecting the end portions of the bridgespan to the adjacent bridge piers, allowing the bridge span to carry itsown weight, disconnecting the end portions of the erection span from thebridge piers, and lowering the erection span.

5. In a method as in claim 4 together with the additional steps ofutilizing the erection span as a tie member between the two adjacentpiers, adjusting the spacing between the centers of the adjacent piersby utilizing adjust ment means connected to the erection span forpulling the adjacent piers toward each other or pushing them away fromeach other.

6. In a method for the construction of a permanent bridge span betweenadjacent bridge piers wherein the bridge piers have a lower foundationportion and an upwardly extending tower section for permanent attachmentto the bridge span, the method comprising the steps of positioningtemporary supporting bents on the piers in predetermined spacerelationship with the lower ends thereof having load supportingengagement with the foundation portions of the piers, moving an erectionspan into a general position adjacent the two piers, elevating saiderection span until end portions thereof are at an elevation above theupper ends of said bents, providing load supporting engagement betweensaid end portions of the erection span and the upper ends of said bents,progressively constructing the permanent bridge span in a regionoverlying the erection span, the construction commencing at one bridgepier and ending at the next adjacent bridge pier, supporting the bridgespan at panel points upon the erection span, providing camber in thelower chord of the bridge span, and maintaining the camber in the lowerchord of the bridge span as the erection span is progressively loaded bythe progressive erection of the bridge span, adjusting the spacingbetween the bridge towers by operation of adjustable means connectingthe erection span to at least one of the bridge piers and utilizing theerection span as a tie member to cause the pier towers to be pushed awayfrom each other or pulled toward each other to facilitate connecting theend portions of the bridge span to the bridge towers, securing the endportions of the bridge span to the adjacent bridge towers, allowing thebridge span to carry its own weight, removing the temporary supportingbents from the piers, and lowering the erection span between the piers.

7. In a method for the construction of a permanent bridge span betweenadjacent bridge piers wherein the bridge piers have a lower foundationportion and upwardly extending tower sections for permanent attachmentto the bridge span, the method comprising the steps of positioningtemporary supporting bents on the piers in predetermined spacerelationship with the lower ends thereof having load supportingengagement with the foundation portions of the piers, moving an erectionspan into a general position adjacent the piers, the erection span beingfabricated of a relatively light material in comparison to steel,hoisting the bridge span at an angle with respect to the center line ofthe bridge piers to a level above the upper ends of the supporting bentsby using a traveler mounted on the previously completed bridge spans forhoisting one end of the erection span and a floating derrick barge forhoisting the other end of the erection span, causing engagement of theshoe means on one end portion of the erection span with the seatingmeans carried by the upper end of the adjacent supporting bent,adjusting the lateral position of the shoe means on the other endportion of the erection span to overlie the seating means carried by theupper end of the adjacent supporting bent, the adjustment being made byadjustable means carried by the erection span, causing engagement of thelast named shoe means with the last named seating means, restoring theadjustable means to a normal position, progressively constructing thebridge span in a region overlying the erection span, the constructioncommencing at one bridge pier and ending at the adjacent bridge pier,supporting the bridge span upon the erection span at panel points on thebridge span along the length of the bridge span, providing camber in thelower chord of the bridge span, maintaining the camber in the lowerchord of the bridge span as the erection span is progressively loaded bythe progressive erection of the bridge span, adjusting the spacingbetween the bridge towers by operation of the adjustable means carriedby the erection span and utilizing the erection span as a tie member tocause the pier towers to be pushed away from each other or pulledtowards each other to facilitate connecting the end portions of thebridge span to the bridge towers, connecting the end portions of thebridge span to the adjacent bridge towers, allowing the bridge span tocarry its own weight, hoisting the erection span to cause disengagementof the shoe means and the seating means, removing the temporarysupporting bents from the piers, and lowering the erection span betweenthe piers by using the traveler mounted on the bridge span justcompleted.

8. Apparatus for constructing a bridge span between two adjacent bridgepiers, each of the bridge piers having a lower foundation portion, theapparatus comprising temporary supporting bents adapted to be mounted onthe piers in a predetermined space relationship with the lower endsthereof adapted to rest on the lower foundation portion of the piers, anerection span, the erection span being fabricated of a materialsubstantially lighter than steel and being of a length that will fitbetween adjacent bridge towers, means adapted to connect the endportions of the erection span to the upper ends of the supporting bents,the bridge span being erected in a region overlying the erection span,and jacking means resting upon the erection span and adapted to supportthe bridge span at predetermined panel points, the jacking means beingcontrolled so that a camber is provided and maintained in the lowerchord of the bridge span as the erection span is progressively loaded bythe progressive erection of the bridge span.

9. Apparatus for constructing a bridge span between two adjacent bridgepiers, the bridge piers having a lower foundation portion, the apparatuscomprising temporary supporting bents adapted to be mounted on the piersat a predetermined space relationship with the lower ends thereofadapted to rest on the lower foundation portions of the piers, anerection span, the erection span being fabricated of a materialsubstantially lighter than steel, seating means having conical recessesmounted on the upper portions of the temporary supporting bents, conicalshoe means mounted on the end portions of the erection span and adaptedto nest within said seating means, adjustable means mounted on theerection span for moving at least one of the shoe means in a directionlongitudinally of the erection span to facilitate nesting of the shoemeans within the seating means, the bridge span being erected in aregion overlying the erection span, and jack means resting upon theerection span and adapted to engage the bridge span at predeterminedpanel points for providing a camber in the lower chord of the bridgespan and for maintaining the camber in the lower chord of the bridgespan as the erection span is progressively loaded by the progressiveerection of the bridge span upon the erection span.

10. Apparatus as in claim 9 wherein the means for moving the shoe meanslongitudinally consists of a toggle mechanism.

11. Apparatus as in claim 9 wherein the temporary supporting bents areprovided with pin connected shoes to eliminate bending moment.

12. Apparatus as in claim 9 wherein the jack means permits horizontalmovement between the bridge and erection spans.

13. Apapratus for constructing a bridge span between adjacent bridgepiers, the bridge piers having a lower foundation portion and an uppertower portion, the apparatus comprising base shoes adapted to be mountedon the lower foundation portions, temporary substantially verticalsupporting bents having their lower ends pivotally connected to the baseshoes, beam shoes pivotally connected to the upper ends of the temporarysupporting bents, substantially horizontal beams fixed to the beam shoesand secured to the tower portions of the piers, the supporting bentsproviding vertical support only and the beams providing lateral support,an erection span, the erection span being fabricated of a materialsubstantially lighter than steel, conical seating means formed withinsaid beams, conical shoe means pivotallly mounted on the end portions ofsaid erection span and being adapted to nest in said conical seatingmeans, means mounted on said erection span for moving at least one ofsaid conical shoe means in a direction longitudinally of the erectionspan to facilitate nesting of the conical shoe means in the conicalseating means, the bridge span being erected in a region overlying theerection span, and jack means resting on the erection span and adaptedto support the bridge span at predetermined panel points to provide acamber in the lower chord of the bridge span, said last named meansbeing adjustable to maintain the camber in the lower chord of the bridgespan as the erection span is progressivelp loaded by the progressiveerection of the bridge span upon the erection span.

14. In a method for construction of a permanent bridge span betweenadjacent bridge piers, the method comprising the steps of moving anerection span into a genera position adjacent the bridge piers, theerection span being fabricated of a relatively light material incomparison to steel, hoisting the erection span to a predeterminedReferences Cited in the file of this patent UNITED STATES PATENTS1,967,827 Leake July 24, 1934 1,970,966 Leake Aug. 21, 1934 2,692,034Tidwell Oct. 19, 1954 OTHER REFERENCES Engineering News-Record, Sept, 2,1954 (page 31 relied on). Copy in Scientific Library and in Div. 33.

